Nitrogen-vacancy ensemble magnetometry based on pump absorption
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2018-01-11 |
| Journal | Physical review. B./Physical review. B |
| Authors | Sepehr Ahmadi, Haitham A. R. El-Ella, Adam M. Wojciechowski, Tobias Gehring, J. Bindslev Hansen |
| Institutions | Technical University of Denmark |
| Citations | 22 |
| Analysis | Full AI Review Included |
Technical Analysis & Documentation: NV Ensemble Magnetometry via Pump Absorption
Section titled âTechnical Analysis & Documentation: NV Ensemble Magnetometry via Pump AbsorptionâThis documentation analyzes the research demonstrating Absorption Detected Magnetic Resonance (ADMR) in MPCVD diamond for high-sensitivity magnetic field sensing, highlighting how 6CCVDâs specialized materials and processing capabilities are essential for achieving the projected pT/&sqrt;Hz performance.
Executive Summary
Section titled âExecutive Summaryâ- Novel Sensing Method: The research validates Nitrogen-Vacancy (NV) ensemble magnetometry using Absorption Detected Magnetic Resonance (ADMR) within a resonant optical cavity. This approach detects spin-polarization dependent changes in pump light absorption, circumventing the low efficiency associated with fluorescence collection (ODMR).
- Measured Performance: A low-frequency magnetic noise floor of approximately 100 nT/&sqrt;Hz was achieved over a 125 Hz bandwidth using a chemical vapor deposited (CVD) single-crystal diamond.
- Projected Shot-Noise Limit: By optimizing the $\text{NV}^{-}$ concentration and utilizing cavity reflection monitoring near the impedance-matched point, the system is projected to reach a photon shot-noise-limited sensitivity of $\sim 1 \text{ pT}/\sqrt{\text{Hz}}$.
- Material Limitation Identified: The current âoff-the-shelfâ diamond sample (0.16 ppb native $\text{NV}^{-}$) showed that non-NV related processes dominate the optical propagation loss ($\alpha_{\text{abs}} \sim 0.0301 \text{ mm}^{-1}$), indicating a need for higher purity and precise doping control.
- 6CCVD Value Proposition: Achieving pT sensitivity requires custom SCD material with controlled, uniform $\text{NV}^{-}$ densities (optimally $\sim 70.8 \text{ ppb}$) and ultra-low background nitrogen/impurity levels, coupled with high-precision polishing and custom geometryâall core specialties of 6CCVD.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the ADMR experiments and simulations:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Laser Pump Wavelength | 532 | nm | NV center excitation |
| Diamond Type Used | Native $\text{14NV}$ Single Crystal | N/A | CVD grown, off-the-shelf |
| Measured Noise Floor | $\sim 100$ | nT/$\sqrt{\text{Hz}}$ | Achieved sensitivity at 0.4 W pump power |
| Measurement Bandwidth | Up to 125 | Hz | Limited by lock-in filter roll-off |
| Projected Optimal Sensitivity | $\sim 1$ | pT/$\sqrt{\text{Hz}}$ | Shot-noise limit (reflected power mode) |
| Current $\text{NV}^{-}$ Concentration | $2.9 \times 10^{10} \text{ mm}^{-3}$ | (0.16 ppb) | Concentration in tested sample |
| Optimal Projected $\text{NV}^{-}$ Concentration | $\sim 70.8$ | ppb | Required concentration for 1 pT/$\sqrt{\text{Hz}}$ |
| Diamond Thickness (l/2) | 1.3 | mm | Round-trip path is $2 \times 1.3 \text{ mm}$ |
| Non-NV Absorption Loss ($\alpha_{\text{abs}}$) | $\sim 0.0301$ | $\text{mm}^{-1}$ | Dominates propagation loss in tested sample |
| Unloaded Cavity Finesse (F) | $114 \pm 0.1$ | N/A | Theoretical maximum |
| Loaded Cavity Finesse (F) | $45.1 \pm 0.1$ | N/A | Reduced due to diamond inclusion |
| Optimal Rabi Frequency ($\Omega$) | $0.21$ | MHz | For 1 pT/$\sqrt{\text{Hz}}$ projection (P$_{in}=0.5 \text{ W}$) |
Key Methodologies
Section titled âKey MethodologiesâThe experiment utilized a novel cavity-based ADMR technique designed to maximize the detection contrast of the spin state transition:
- Material Preparation: An off-the-shelf single-crystal CVD diamond with native $\text{14NV}$ concentration ($\sim 0.16 \text{ ppb}$) was used.
- Optical Setup: The diamond was placed inside a resonant optical cavity (confocal configuration) with specific mirror reflectivities ($R_1 \approx 94.8%$, $R_2 \approx 99.8%$) and operated at the Brewster angle ($\theta \sim 67^{\circ}$) to minimize reflection losses.
- Excitation: A 532 nm pump laser was used to excite the NV centers, and the MW drive field modulated the spin population between the $m_{\text{s}}=0$ and $m_{\text{s}}=\pm 1$ sublevels.
- Detection Method (ADMR): The measurement was based on monitoring the change in the pump-light absorption (which is spin-dependent) via the light transmitted through the cavity.
- Noise Suppression: Low-frequency technical noise was mitigated by tapping a reference light signal before the cavity and subtracting the photocurrents using lock-in detection based on a frequency-modulated MW drive.
- Optimization Strategy: High-sensitivity measurements were achieved by performing three-frequency excitation (mixing modulation frequency $f_c$ with $f_m = A_{||}$ signal) to simultaneously drive all three $\text{14N}$ hyperfine transitions.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâReplicating and, critically, extending this foundational research to the projected pT/$\sqrt{\text{Hz}}$ sensitivity requires ultra-high-quality, custom-engineered diamond material. 6CCVD is uniquely positioned to supply the necessary next-generation substrates.
Applicable Materials for Picoscale Sensitivity
Section titled âApplicable Materials for Picoscale SensitivityâThe paper demonstrated that achieving the ultimate shot-noise limit hinges on optimizing the $\text{NV}^{-}$ concentration (required $70.8 \text{ ppb}$) and minimizing non-NV related absorption ($\alpha_{\text{abs}}$). 6CCVD offers two primary material solutions:
| 6CCVD Material | Recommended Grade & Specification | Application Suitability |
|---|---|---|
| Single Crystal Diamond (SCD) | High Purity Optical Grade (Type IIa/Ib, specific doping) | Primary Choice. SCD is necessary for high-coherence, low-loss optical cavity applications. 6CCVD provides precise in-situ nitrogen doping during MPCVD growth to achieve target concentrations up to $100 \text{ ppb}$ range, ensuring the required $70.8 \text{ ppb}$ NV density is uniform. |
| Polycrystalline Diamond (PCD) | Not Recommended for ADMR Cavity | While 6CCVD offers PCD plates up to $125 \text{ mm}$, the residual grain boundaries and increased scattering losses ($\alpha_{\text{r}}$) render PCD unsuitable for low-loss, high-finesse optical cavity experiments described herein. |
Customization Potential
Section titled âCustomization PotentialâThe success of the cavity-based ADMR relies on tight tolerances for geometry, surface quality, and material integration.
| Research Requirement | 6CCVD Customization Service | Technical Benefit |
|---|---|---|
| Optimized $\text{NV}^{-}$ Density | Custom SCD Growth (Controlled $\text{N}_{2}$ flow) | Achieve projected $70.8 \text{ ppb}$ concentration, maximizing spin contrast while managing self-absorption. |
| Minimized Non-NV Loss ($\alpha_{\text{abs}}$) | Ultra-High Purity MPCVD Growth | Reduce unintentional background impurities (e.g., substitutional $\text{N}_{s}$, vacancies) that contribute to optical loss, currently dominating the sampleâs absorption. |
| Precise Geometry (Brewster Angle) | High-Precision Laser Cutting / Shaping | Custom dimensions (e.g., $1.3 \text{ mm}$ thickness plates) and specific angled facets can be fabricated to reduce insertion loss and match cavity specifications perfectly. |
| Surface Loss Mitigation ($\alpha_{\text{r}}$) | Advanced Polishing (Ra < 1 nm for SCD) | Ensure ultra-smooth surfaces to minimize scattering losses and surface-based absorption in the high-finesse optical cavity. |
| Device Integration | Custom Metalization (Ti/Pt/Au, etc.) | While not specified here, if future iterations require MW antennas or electrodes integrated directly onto the SCD surface, 6CCVD offers in-house $\text{Au}$, $\text{Pt}$, $\text{Pd}$, $\text{Ti}$, $\text{W}$, and $\text{Cu}$ metalization capabilities. |
Engineering Support
Section titled âEngineering SupportâThe transition from $100 \text{ nT}/\sqrt{\text{Hz}}$ to $1 \text{ pT}/\sqrt{\text{Hz}}$ requires deep expertise in diamond material physics and CVD growth control. 6CCVDâs in-house PhD team specializes in optimizing diamond parameters for demanding quantum applications. We offer comprehensive engineering consultations to assist researchers in selecting the precise nitrogen doping level, managing defect conversion ratios, and defining stringent polishing specifications necessary for high-finesse cavity NV Magnetometry projects.
Call to Action: For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
We demonstrate magnetic field sensing using an ensemble of nitrogen-vacancy centers by recording the variation in the pump-light absorption due to the spin-polarization dependence of the total ground state population. Using a 532 nm pump laser, we measure the absorption of native nitrogen-vacancy centers in a chemical vapor deposited diamond placed in a resonant optical cavity. For a laser pump power of 0.4 W and a cavity finesse of 45, we obtain a noise floor of $\sim$ 100 nT/$\sqrt{\textrm{Hz}}$ spanning a bandwidth up to 125 Hz. We project a photon shot-noise-limited sensitivity of $\sim$ 1 pT/$\sqrt{\textrm{Hz}}$ by optimizing the nitrogen-vacancy concentration and the detection method.